The present invention will be illustrated with reference to a paging system (the "Gaskill system") described in U.S. Pat. Nos. 4,713,808 and 4,897,835. However, it will be understood that the present invention is not limited to such context of use. The disclosures of U.S. Pat. Nos. 4,713,808 and 4,897,835 are incorporated herein by reference.
The Gaskill system incorporates paging devices into wristwatches. Paging information, together with high precision time of day information, is transmitted by FM radio signal to each paging device according to a time-multiplexed protocol. In accordance with this protocol, each paging device includes a timing mechanism activating a radio receiver and decoder of the watch-pager during a particular time slot. The watch-pager thereby activates its radio receiver and decoder to capture the radio signal data broadcast during a selected time slot.
In a conventional time piece, even the slightest inaccuracy in time keeping accumulates. The extent of error, i.e., deviation from a standard or common time reference, grows over time. For example, with a group of conventional digital display time pieces placed side by side, the least significant digits, e.g., the seconds digits, do not change in synchronization. Even if conventional time pieces are set initially to identical time, the slightest inaccuracy or relative inconsistency in time keeping accumulates and makes impossible synchronized time display for an extended period.
Time piece inaccuracy is observed, therefore, by inspecting the time display of a number of devices placed side by side. If the time pieces keep accurate time, simultaneous display updates by all time pieces will endure. For example, the seconds display for all devices change simultaneously. Typically, however, such simultaneous display updating is not achieved, and if achieved does not endure.
In a digital time piece in the form of a wristwatch, a processing unit manages such operations as extracting time of day information from a counter register and maintaining or updating a display synchronously at, for example, whole second intervals, i.e., the least significant display digit changes precisely at given intervals. A conventional time piece operating in this fashion dedicates entirely the processor resources to the simple task of retrieving time of day information from a counter register and updating the display and rarely the operation of user buttons to set time, activate a light, etc.
In a paging device incorporating a time piece and time display, however, the processing unit must also devote its processing resources to the significant tasks of managing incoming paging messages and related decoding, error checking, and frequent user interaction in displaying received paging messages. Accordingly, the time display function in such a paging device must share processor resources with the paging message receiving and processing functions. Unfortunately, this shared processing resource is necessarily limited in its processing power. Generally, processing elements available for use in such devices, i.e., a paging device incorporated into a small product such as a wristwatch, is a relatively weak processing element in its data width, clock speed and power consumption. While much more powerful processing elements, e.g., desktop personal computers, could more easily orchestrate the tasks of time maintenance and display and paging message processing and display, the processing element required in a small device such as a watch-pager device is challenged when faced with the combined tasks of time maintenance and display, paging message processing and display, and user interface support. Accordingly, such processing element may be incapable of providing synchronous time display updates relative to other similar time pieces, i.e., a group of such devices placed side by side would likely have non-synchronous transition in the seconds digit of the time display.
As may be appreciated, a paging device operating under a time multiplexed protocol and standing ready to interact with a user operating control buttons must timely react to interrupts generated by such activity. Such interrupt handling routines, however, can take enough processing time to affect time display updates. In other words, the processor may potentially be interrupted and unavailable at a time when the time display should be updated. As a result, time display updates may not always occur precisely at whole second intervals. To maintain display updates synchronously within human perception, the display updates must occur within a given time interval relative to one another. For example, human perception can detect time display updates offset by as much as one-tenth of a second. In a weak processing element managing both paging functions and time maintenance and display functions the time display function can be perceivably delayed, i.e., delayed by as much as or more than one-tenth of a second.
A paging device including time keeping and display functions desirably provides accurate time display wherein a group of such devices exhibits such accuracy by continued simultaneous time display updating. The subject matter of the present invention provides such a time display update capability.